Classicly

The other twelve will come some day, my boy; at present you have the right number of teeth for a child of your age. They do not all come at one time, but one after another. We begin with twenty, and no more. They are called milk teeth, or first teeth. When we are about seven years old they begin to fall out and are replaced by others stronger and set in more firmly. In addition to this second score of teeth there appear later twelve others, bringing the total number up to thirty-two. Those farthest back, in the inmost cavity of the mouth, come late, when we are eighteen or twenty years old, or even older, for which reason they are called wisdom teeth to signify that they appear at an age when the reason is well developed. These thirty-two last teeth constitute the second cutting. I call them last because they are never replaced by any others; if we lose them, that is the end of our teeth; no more will come